1. Field of the Invention
The present invention relates to an internal combustion engine equipped with a variable valve control system. More particularly, the present invention relates to an internal combustion engine in which certain selected valves are operable by two different camshafts, which are alternately selectable with a rocker arm to control operation of the valve.
2. Description of the Background Art
A conventional internal combustion engine is known which has been designed to switch between alternate valve actions by use of a rocker arm. The rocker arm is pivotally supported on a rocker arm shaft which is slidably movable in an axial direction thereof. The rocker arm is disposed to selectively link an engine valve with a first or second cam that serves the engine valve. By axially sliding on the rocker arm shaft, the rocker arm selectively engages with one of the two cams to switch the valve actions (see, for example, Patent Document 1).
This known variable valve control system includes an engagement member which is pivotally attached to the rocker arm; a lock groove formed in the rocker arm shaft; and a protruding portion formed on the bottom of the lock groove. At the timing of actions (swings) of the rocker arm while the engine is running at a predetermined speed or faster, the protruding portion flips the engagement member up, so that at these higher speeds of operation, a restriction on the sliding movement of the rocker arm is removed, where such restriction is otherwise imposed by the engagement of the engagement member at lower engine speeds.
[Patent Document 1] JP-A-62-184117
In the above-described conventional configuration, the inertial force generated by the flipping up of the engagement member by the protruding member is used to remove the restriction imposed by the engagement member on the sliding movement of the rocker arm. The inertial force differs, depending on the swinging speed of the rocker arm and accordingly the angular velocity of the rotating cam (which is proportional to the engine speed). The difference in the inertial force sometimes varies the timings at which the restriction imposed on the sliding movement is removed. For this reason, the conventional technique is applicable to engines of limited conditions (i.e., a limited engine-speed range).
An object of the present invention, therefore, is providing an internal combustion engine equipped with a variable valve control system which switches the actions of an engine valve by sliding a rocker arm in the axial direction of the rocker arm shaft and which is capable of removing the restriction on the sliding movement of the rocker arm in accordance with the timings of the actions of the rocker arms irrespective of the engine speed.